Holdren outlined several "tipping points" involving global warming that could be fast approaching.

Once such milestones are reached, such as complete loss of summer sea ice in the Arctic, it increases chances of "really intolerable consequences," he said.

Twice in a half-hour interview, Holdren compared global warming to being "in a car with bad brakes driving toward a cliff in the fog."

At first, Holdren characterized the potential need to technologically tinker with the climate as just his personal view. However, he went on to say he has raised it in administration discussions.

Holdren, a 65-year-old physicist, is far from alone in taking geoengineering more seriously.

The National Academy of Science is making climate tinkering the subject of its first workshop in its new multidiscipline climate challenges program.

The British parliament has also discussed the idea.

The American Meteorological Society is crafting a policy statement on geoengineering that says "it is prudent to consider geoengineering's potential, to understand its limits and to avoid rash deployment."

Last week, Princeton scientist Robert Socolow told the National Academy that geoengineering should be an available option in case climate worsens dramatically.

But Holdren noted that shooting particles into the air — making an artificial volcano as one Nobel laureate has suggested — could have grave side effects and would not completely solve all the problems from soaring greenhouse gas emissions.

So such actions could not be taken lightly, he said.

Still, "we might get desperate enough to want to use it," he added.

Another geoengineering option he mentioned was the use of so-called artificial trees to suck carbon dioxide — the chief human-caused greenhouse gas — out of the air and store it.

At first that seemed prohibitively expensive, but a re-examination of the approach shows it might be less costly, he said.